Field of the Invention
Embodiments of the present application relates to the art of a drive motor used as a prime mover of automobiles, and especially to a motor drive unit having a power transmission device between the drive motor and drive wheels.
Discussion of the Related Art
PCT international publication WO 2015/008661 describes one example of a motor drive unit of this kind. The drive gear unit taught by WO 2015/008661 as a torque vectoring device comprises a differential unit for distributing torque delivered from a drive motor to right and left drive wheels, and a differential motor for controlling a torque split ratio to the drive wheels. The differential unit comprises a pair of single-pinion planetary gear units, and sun gears of the planetary gear units are connected to both ends of a rotary shaft. An input gear is fitted onto an intermediate portion of the rotary shaft, and torque of the drive motor is applied to the input gear. Ring gears of the planetary gear units are connected to each other through a torque reversing device so that the ring gears are rotated in opposite directions. The differential motor is connected to one of the ring gears, and drive wheels are connected the carriers of the planetary gear units.
A driving performance of an electric vehicle may be improved by using the torque vectoring device taught by WO 2015/008661 as a motor drive unit. The motor drive unit of this kind may serve as an inboard brake by incorporating a brake device into the motor drive unit to apply brake torque to the drive wheels. To this end, for example, an electromagnetic brake may be used in the motor drive unit. In this case, a hydraulic system and reinforcements such as a brake caliper and so on may be omitted, and hence the motor drive unit may be downsized and lightened. In addition, an unsprung load of the vehicle may be reduced.
However, in the torque vectoring device taught by WO 2015/008661, an output torque of the drive motor is applied to the input gear disposed on the width center of the vehicle. To this end, the drive motor has to be disposed on one side of the vehicle. In the motor drive unit, a weight of the drive motor is relatively larger than those of other members and this may cause a disruption of a weight balance of the vehicle. In the conventional motor drive unit, therefore, it is preferable to arrange the brake motor in such a manner as to maintain weight balance of the vehicle.